A propulsion device for a marine motor is often incorporated with a clutch mechanism that can be shifted to a forward, reverse and neutral condition as desired. A typical propulsion device for an outboard marine motor includes a drive shaft extending vertically and connected to a crankshaft of an internal combustion engine at an upper end, a drive bevel gear fixedly attached to a lower end of the drive shaft, a propeller shaft extending horizontally adjacent to the lower end of the drive shaft, a pair of driven bevel gears supported coaxially to the propeller shaft in a freely rotatable manner and meshing with the drive bevel gear so as to rotate in mutually opposite directions and a pair of clutch devices that engage a selected one of the driven bevel gears with the propeller shaft. See Japanese patent laid open publication No. 2003-205891 (Patent Document 1), for instance.
The clutch devices disclosed in Patent Document 1 each consist of a multi-disk clutch device which is relatively complex and occupies a relatively large space. Furthermore, each clutch device is actuated by hydraulic pressure, and this requires an oil circuit for each clutch device. These factors result in a highly level of complexity and an excessive space requirement. A high manufacturing cost is also a problem.
Propulsion devices using manually operated dog clutches for shifting a power transmission mechanism is also known, but a large manual force is required for its operation, and this impairs the convenience of the outboard marine motor.